HEAT-STABLE ANTIGEN (MOUSE CD24) IN THE BRAIN - DUAL BUT DISTINCT INTERACTION WITH P-SELECTIN AND L1

Heat-stable antigen (HSA/mouse CD24) is expressed in both haematopoiet ic and neural cells. The small core protein of the molecule is extensi vely glycosylated and anchored to the membrane via glycosylphosphatidy linositol. The role of HSA in the developing brain as well as its func tional properties are poorly understood. Here we show that the brain H SA is associated with N- and O-linked oligosaccharide moieties and dec orated with the HNK-1 sulfated carbohydrate epitope. It can bind P-sel ectin but not E-selectin and this interaction requires divalent cation s and is sensitive to high salt. Brain-derived HSA is also capable of binding to the L1 adhesion molecule, This interaction is distinct from the P-selectin binding as it is resistant to high salt and does not r equire bivalent cations. Treatment of HSA with OSGE significantly redu ced binding of both P-selectin and L1. Our data suggest that HSA can b ind P-selectin and L1 by distinct mechanism and that the binding epito pes on HSA are in close proximity.